1. Field of the Invention 
The invention relates to shoes or boots having an outsole adapted for walking on sand. 
2. Description of the Related Art 
Exploration for oil, oil production, pipeline and electric grid service, and military deployment is increasingly occurring in desert regions, which requires personnel to walk confidently on sand. Existing work shoes and military boots are not well suited for this type of terrain. They cut easily through the sand surface, push the sand aside from under the sole with ease, and sink deeply prior to providing sufficient support and grip. A typical example is the desert boot specified by United States military specification MIL-B-4315M Type II. This boot features deeply grooved and slotted treads, peripheral openings in the tread, sharp outsole edges, and a generally convex outsole.  
Although the sole provides good grip on semi-hard and hard soil or rocks, these features make it unsuitable for use in sand. For instance, the ridges cut easily into sand and the convex sole and wide grooves push the sand away from the boot. The result is that the wearer sinks into the sand. This wastes energy, thereby reducing on-foot mobility and increases the risk of heat related injuries in hot desert weather. 
One solution is disclosed in U.S. Pat. No. 3,082,548 by Hartman, which is not admitted to being prior art by its mention in this Background section. Hartman discloses a strap-on sand shoe having compaction pockets that help prevent the user from sinking into sand. The soles of the strap-on shoes extend well beyond the soles of the wearer”s normal shoes, and bend in only one place. In addition, the ridges forming the compaction pockets are beveled inward, which tends to push sand out from under the shoe rather than trapping it underneath. Because the Hartman shoes are strap-on, they do not appear to be suitable for continuous duty by foot soldiers. 
Another solution is disclosed in U.S. Pat. No. 4,094,081 by Reiner et al., which is not admitted to being prior art by  its mention in this Background section. Reiner discloses a beach sandal having a cupped sole. The sole ridges containing the sand are beveled outward to better retain sand and support the user. However, it is also a strap-on shoe that appears cumbersome and is unsuitable for military use. Additionally, the Reiner sandal does not have a raised heel, which would be a disadvantage when using ladders or operating equipment. 
Yet another solutions is disclosed in two patents by Johnson, U.S. Pat. Nos. 4,447,969, and 4,566,209, which are not admitted to being prior art by their mention in this Background section. The Johnson patents disclose add-on wings and webs to boots for walking on sand and loose material. The extra hardware expands with springs and hinges when the boots sink into sand. Presumably, the user would be as fleet of foot as the Roman god Mercury on his talaria. This is unlikely, especially in military applications, due to their sheer complexity and awkwardness. 
What is needed, therefore, is a desert boot outsole for supporting the user in sand that does not require strap-on hardware and can be used on ladders and equipment. 